Get the Sigma 50mm 1.4. That way you have a top quality prime lens that has excellent bokeh, is fast and is useful for many situations. Portraits, environmental portraits, kids etc.
Then get the Tamron 28-75mm f/2.8 zoom. Can be had for ridiculously good prices, has same image quality has the Canon 24-70mm L lens and again is fast and provides nice shallow depth of field.
Obviously the 28-105mm has a little extra reach but personally I don't think it's such a great lens especially if you like shallow depth of field. You can have the 2 above lenses for less than the price of the single Canon. Plus if you would be comfortable with the image quality of the Canon 50mm 1.8 then there is no point shelling out all that money on the Canon L lens when there is equally as good alternatives for much less.
In fact I am pretty sure you could get the Sigma 50mm and then one of those mega range zooms (like 25 - 300mm or something) from Sigma or Tamron for the same as the Canon lens.
Rob Meredith